The increased sophistication and use of genetic susceptibility testing and prescreening tests in a variety of medical settings has created special challenges for both patients and health care providers. Patients must grapple with information regarding the purpose and outcomes of these tests, decide whether to have a test which may ultimately provide results associated with a degree of uncertainty, as well as understand the implications of these tests. Patients may be offered such testing at a time when they are already faced with unwanted news about their own health. Providers are faced with the challenge of not only understanding the intricacies of the test, but also educating patients about them. An illustrative context in which to explore these issues is the evaluation of patients suspected of having hereditary non-polyposis colorectal cancer (HNPCC). HNPCC is caused by germline mutations in several DNA mismatch repair genes. However, for most individuals at risk, a prescreening test is recommended before germline mutation analysis. Microsatellite Instability (MSI) is a phenotype associated with mutations in the culprit mismatch repair genes. MSI testing of a patient's tumor is now recommended as an initial screen to determine whether individuals are likely to carry mutations associated with HNPCC. MSI is graded as high, low or stable (none). Patients with MSl-high tumors are referred for genetic testing for germline mutations. Very little is known about the adequacy of the informed consent process for this test. At Fox Chase Cancer Center, patients are provided with an explanation of MSI by their physician and a one-page written consent form. Our pilot study indicated that patients have little objective knowledge about what MSI testing actually entailed. Participants wanted more information about the MSI test and did not feel adequately informed to make the decision. The goal of the proposed study is to develop a CD-ROM intervention to enhance the level of knowledge about MSI testing and facilitate decision-making, and to test this CD-ROM intervention in a randomized clinical trial design. We will evaluate the impact of the intervention on knowledge about MSI as well as on perceived satisfaction with the preparation to make the decision. We will also evaluate the impact of the intervention on traditional decisional outcomes including decisional satisfaction, difficulty making the decision to have the test, and decisional conflict, as well as the impact on attitudes about MSI testing, cancer worries and perceived CRC risk. The CD-ROM intervention will be developed with a view towards future dissemination.